We are pursuing an in-depth investigation on the structure and function of the plasma membrane receptor for immunoglobulin E. (IgE). Most of the work utilizes a cell line called rat basophilic leukemic cells recently found to represent a tumor analog of mucosal-type mast cells. During the past year we have focussed on the following subjects: 1) continued characterization of the subunits of the receptor. In particular, we performed additional studies on the isoelectric point, size, and multiplicity of the gamma chains of the alpha, bets, (gamma)n complex. We have essentially completed a compositional analysis of ecah of the chains using both in vivo incorporaton protocols and amino acid analysis. We also examined the relationship between the subunits using analysis by high pressure liquid chromatography of tryptic and chymotryptic digests of each of the chains. 2) continued attempts were made to obtain peptides in sufficient quantities to perform sequence analysis in preparation for making cDNA probes. 3) Continued attempts were made to generate monoclonal antibodies which can be used to probe the topology of the peptides in the plasma membrane. 4) Functional studies during the past year have focussed on attempts to analyze the hydrolysis of (poly)phosphosinositides that occurs as a consequence of aggregation of the receptors for IgE. In particular, various types of altered cells or cell-free preparations have been examined such as saponized cells, cytoblasts, and membrane preparations.